A conventional LCD pixel is three sub-pixels: red, green and blue. An M+ panel adds a fourth, white sub-pixel. Because white light does not have to be filtered through a colour, far more of the backlight reaches the viewer — white luminance rises by roughly 50% at the same backlight power.
That is the headline, but it is not the reason we use it for window displays. The M+ structure we build with is blackening free: the panel does not darken behind heated glass. Anyone who has installed a standard commercial display in a sunlit window has watched that happen — a grey cast that creeps in from the edges on the first hot afternoon and does not fully recover.
The second reason is the circular polarizer. A conventional linear polarizer means the display goes black for anyone wearing polarized sunglasses at the wrong angle. Outdoors and street-facing, that is a large share of your audience. A circular polarizer keeps the image visible regardless of head angle.
